The Plasmonic Effect of Gold Nanorods on Charged Molecules: SERRS and SEF effects

Abstract

Target molecules adsorbed onto metallic nanoparticles can have their Raman and/or fluorescence signals enhanced, leading to the called surface-enhanced [resonance] Raman scattering (SE[R]RS) or surface-enhanced fluorescence (SEF). Here we have applied Au nanorods (AuNRs) coated with a surfactant bilayer leading to a positive surface charge to investigate the role played by these AuNRs in colloidal suspension on SERRS and SEF effects of charged molecules. In the case of the anionic nickel (II) tetrasulfonated phthalocyanine (NiTsPc), besides achieving SERRS with an enhancement factor (EF) of ca. 10 5 , the AuNRs allowed the analytical application of the SERRS effect for the NiTsPc between 8.3x10 -6 and 4.0x10 -5 mol L -1 . The limit of detection of 4.8x10 -7 mol L -1 (at 752 cm -1 ) and 1.3x10 -6 mol L -1 (at 1338 cm -1 ) was found. In the case of the cationic methylene blue, the SEF effect was achieved reaching an EF of ca. 10. Besides, fundamental discussions are carried out considering the results presented here.

Potential of electrolyte-gated transistors for anionic molecule detection: proof of concept using dye solution

“…As the detection of anionic analytes via SERS in colloidal systems often faces limitations [22], then the use of EGTs platform can be a promising alternative to detect such molecules. To achieve the SERS effect and detect the molecule at low concentrations, it is necessary to modify the surface charge of the substrates, making them positively charged, as demonstrated by Oliveira et al [24].…”

“…Several target-molecules have been detected at low concentrations using surface-enhanced Raman spectroscopy (SERS) with negatively charged colloidal dispersion of silver (Ag) or gold (Au) [22,23]. However, in some cases, the negative targetmolecules cannot adsorb onto the surface of metal nanoparticles due to electrostatic repulsion, resulting in a poor enhancement factor (EF) [24]. Therefore, the functionalization of nanoparticles is necessary to enhance the Raman signal [25].…”